1. Field of the Invention
This invention relates to a heat-treating method of a thermoplastic resin film, in which a produced film can be used for structural materials, materials for electronic components and so on.
2. Description of the Related Art
After a thermoplastic resin film is conducted with, for example, simultaneous biaxial orientation, the oriented film is removed with residual stress caused by deformation of the orientation by being heat-treated.
In a conventionally typical heat-treating method, the film is moved while both ends of the film in a direction transverse to the longitudinal direction are fixed in a heating-atmosphere. According to the aforementioned heat-treating method, however, a stress easily concentrates in parts, especially, the stress concentrates in a part where a fish eye, a gel or the like is produced on the film, so that the film is ripped sometimes. Provided that the film is heat-treated at an approximate melting point, the film has a thermal deformation, resulting in a disadvantage that the heat-treatment at an approximate melting point cannot be carried out.
Japanese Patent Application Laid-open No. Sho59-178223 proposes a method, in which an oriented thermoplastic film, having an adherent layer on the surface thereof, undergoes annealing while being attached through the adherent layer on a support plate made by stainless steel.
According to the aforementioned heat-treating method, the film is attached on the support plate by way of the adherent layer, so that the film is prevented from rip caused by the concentrated stress, however, another disadvantage is produced.
That is to say, in order to attach the film on the support plate, the film should be formed with the adherent layer, resulting in necessity of a forming process for the adherent layer. The film should be forcibly peeled from the support plate after the heat-treatment, resulting in difficulty in carrying out processes successively. And further, some types of the films are fused to the support plate made of stainless steel, resulting in impossibility of the successive processes.